Medications are known which, with the same dosage, lead to differently high active substance levels between different persons as well as between different types of mammals. This leads to difficulties in the administration of such a medication when the medication has, at the same time, a narrow therapeutic effective range so that even a comparatively small overdosage or underdosage leads to an intoxication or a loss of the therapeutic effect of the medication.
An example of such a medication is the intravenously administered propofol. Propofol is an anesthetic and sedative which can have grave side effects such as respiratory depression, apnea and a drop in blood pressure with the danger of shock when dosages are too high; however, in the case where the dosage is too low, an awakening of the patient from anesthesia can no longer be reliably prevented. As a rule, propofol is often used together with muscular relaxants for anesthesia. For this reason, an underdosage leads to an awakening of the patient, however, because of the relaxed state of the patient, the patient cannot express this; instead, the patient experiences the further course of the surgical procedure in a state of awakeness which the patient cannot indicate to the attending physicians. While the patient experiences unavoidably the discomfort caused by the surgical procedure, there remains for the patient only the hope that the anesthetist sooner or later recognizes his awakening out of the anesthesia and rapidly reacts correspondingly.
It is true that, for this purpose, the anesthetist has monitors, which are known to the state of the art, for monitoring the depth of anesthesia of a patient and therewith for monitoring the concentration of propofol as described, for example, in U.S. Pat. No. 6,981,947. As described in this patent, the plasma concentration of an intravenously administered medication such as propofol can be determined based on the measurements of breathing gas or can at least be estimated. The anesthetist can therefore be alerted as soon as the concentration of propofol, which is determined in the breathing gas, exceeds or drops below a previously determined concentration range.
This procedure is, however, subjected to disadvantages because the anesthetist, as a rule, only learns of, for example, technical errors when the breathing gas concentration moves out of the determined range. These technical errors can be: malfunctions of a perfuser with which the medication is administered; blocking of a venous access; disturbances of infusion lines or accessories; leakages of such infusions lines or accessories; dislocation of infusion canulas; inadvertent mix-ups of medications; typing errors; defective computations and the like. It can then, however, already be too late to alleviate the technical problems or to increase the dosage of propofol before the patient awakens. It is true that the anesthetist can set the limits of the concentration range as narrow as desired with a warning announcement resulting when there is a movement out of this concentration range. However, the tighter the limits are made, the more often there are false alarms.
These problems occur not only with the above-described intravenous administration of propofol but also during administration of other medications and also when administering the medications via other accesses such as intraarterially, intraperitoneally, intramuscularly, subcutaneously, topically, orally or as inhalant.